1. Field of the Invention
The present invention relates to a retainer for a rolling bearing, and particularly to a retainer for a rolling bearing suitable for supporting rotating member such as hard disk drives, video tape recorders and office automation equipment.
2. Description of the Related Art
As shown in FIG. 2, a ball bearing 10 consists of an inner race 11 and an outer race 12 each having a track surface, and a plurality of balls 5. Each ball 5 is rotatably disposed between the track surfaces of the inner race 11 and the outer race 12 while rotatably retained by a retainer 1. An annular sealing member 13 is arranged at each end of an axial direction.
As shown in FIG. 3, the retainer 1 being an annular body has a plurality of recessed portions 2 disposed at equal spacing and is integrally molded with resin. The recessed portions 2 work for rotatably retaining the balls 5 (refer to FIG. 2) with a pair of claws 3 provided at each of the recessed portions 2 so as to prevent the balls 5 from falling out. Grease reservoirs 4 are arranged between the claws 3 of adjacent recessed portions 2 at a given spacing. The retainer 1 makes it possible to arrange the balls 5 at a given spacing thereby preventing seizure caused by the balls 5 contacting each other.
Since the retainer 1 does not directly support a bearing load, it is not required to use a material having same strength as the material used for the balls 5, the inner race 11, and the outer race 12. However, it is also true that the retainer 1 is in sliding contact with the balls 5, the inner race 11, and the outer race 12. For instance, when the retainer 1 is employed in such a manner that the inner race 11 is rotated while the outer race 12 is still, the balls 5 revolve around the inner race 11 while rotating on its own axis. The retainer 1 receives a driving force from the balls 5 while the balls 5 are in sliding contact with at the recessed portions 2 thereby revolving around the inner race 11 at the same speed as a revolving speed of the balls 5. Accordingly, the retainer 1 is required to be protected from abrasion and seizure, so that it is often made by injection molding using a synthetic resin such as nylon 66.
The retainer 1 molded from such a material can be elastically deformed. Therefore, in the process of injection molding, when a retainer is released from a die after the injected resin therein is solidified, the claws 3, which have an undercut shape to the direction where the retainer is released, are released in such a manner as to be outwardly stretched, namely, a forced pull-out, thereby making possible to simplify the die structure. Moreover, during the assembly of the rolling bearing 10, the ends of the claws 3 of the retainer 1 are outwardly pushed so that the balls 5 can be pushed into the spherical recessed portions 2 to be rotatably supported.
Since above mentioned elements such as easy releasing from the die and easy placement and displacement of the balls 5 from the claws 3 are taken into consideration, the claws 3 are made thin, which leads to the following effects on the rolling bearing 10.
Even though a required clearance is provided between the retainer 1 and the balls 5 or the track races of the inner race 11 and the outer race 12 is filled with grease, a vibration of the retainer 1 is not avoidable generating noise called a retainer noise or vibration. The retainer noise is induced due to the following: (1) self-excited vibration caused by a sliding friction between the balls 5 and the retainer 1; (2) collision between the retainer 1 and the balls 5 due to grease resistance; and so on.
Moreover, a run-out of a revolution frequency of the balls 5 is generated in case each diameter of the balls 5 is different from each other or the balls 5 are not equivalently arranged in the circumferential direction. Thus, when the rolling bearing 10 is rotated, vibration fluctuates resulting in intensifying a non-repetitive run-out (NRRO) causing a minute displacement, which will be the cause of irregular rotation of hard disk drives (HDD), deterioration of characteristics such as NRRO and the like. Used in a high-speed rotation (12,000-15,000 rpm), the thin portion of the retainer 1 tends to be deformed by a centrifugal force from the balls 5, that is, the claws 3 are outwardly stretched giving more space for the balls 5 to move, which increases vibration and the noise of collision between the retainer 1 and the balls 5. Moreover, the balls 5 are largely fluctuated so as to be inequivalently arranged in the circumferential direction aggravating the NRRO.
The present invention has been made in light of the problems described above, namely, the increase of the retainer noise due to the characteristic of the retainer and the aggravation of the NRRO. It is an object of the present invention to provide a retainer having sufficient strength and rigidity so as not to deform by the centrifugal force as well as sliding friction of the rolling elements while keeping characteristics of an easy release of the retainer from a die and also an easy placement and displacement of the rolling elements, thereby preventing a ball bearing from the retainer noise and the aggravation of the NRRO.
In a retainer for a rolling bearing according to a first aspect of the present invention, the retainer is made of resin, comprising pairs of claws for preventing rolling elements from falling off, the pairs of claws equally spaced at a body portion, characterized in that highly-elastic resin is used for part of the body portion which influences the elasticity of the claws. In the present invention there is provided the retainer having sufficient rigidity at the body portion ensuring not only rigidity required for the retainer for the rolling bearing but also elasticity required for the claws. Furthermore, the rigidity of the whole retainer is ensured by using resin with a high elasticity for the part of the claws influencing the elasticity.
In the retainer for the rolling bearing according to a second aspect of the present invention, the body portion is formed of resin having sufficient strength and rigidity preventing deformation due to centrifugal force and sliding friction of the rolling elements. The part influencing the elasticity of the claws is made of highly-elastic resin so that the retainer is easily released from the die while the rolling elements are easily placed and displaced from the claws. Accordingly, the performance of the rolling bearing can be improved by giving a high elasticity to the claws so as to improve the performance of releasing the retainer from the die or placing and displacing the rolling elements from the claws and by ensuring the strength of the whole retainer with the body portion.